1. Field of the Invention
This invention relates to control systems for robotic manipulators and more particularly relates to adaptive control for a plurality of robotic arms, e.g. a multi-arm system in which the cross-coupling between robotic arms through a common load is treated as though it were an externally caused disturbance.
2. Description of the Prior Art
An adaptive control system invented by this inventor is described and claimed in the above-identified application and a considerable number of publications are set forth therein, which publications are incorporated herein by reference as though they were set forth expressly herein. The prior art and references cited therein are called to the attention of the Patent Office as being of background relevance to this invention. As of this filing date, the identified application has received an Office Action and the following patents have been cited; Horack U.S. Pat. No. 4,547,858, Koyama et al U.S. Pat. No. 4,580,229; Sugimoto et al U.S. Pat. No. 4,621,332; and Osuka U.S. Pat. No. 4,725,942. These patents do not have any significant relevance to the invention herein described and claimed.
The system of the identified application is improved upon by being extended from a single arm approach to a dual-arm (or higher) approach with a novel method and apparatus being described for overcoming the cross-coupling that exists in a common load being manipulated by independently controlled manipulators, or arms, in a multi-arm system. Additional background material relevant to the development and a fuller understanding of this invention is given in the following paragraphs.
During the past decade, robot manipulators ("arms") have been utilized in industry for performing simple tasks, and it is foreseen that in the near future anthropomorphic robots will replace human operators in carrying out various complex tasks both in industry and in hazardous environments. Nevertheless, present-day robots can be considered at best as "handicapped" operators due to their single-arm structure. It is evident that a multiplicity of robot arms yields greater dexterity and increased efficiency and provides capability of handling larger loads. Dual-arm robots will therefore have capabilities which may match those of ambidextrous human operators in dexterity and efficiency.
The research on dual-arm robots is at its early stages at the present time and a few approaches are currently available. E. Nakano et al., Cooperational Control of the Anthropomorphous Manipulator MELARM, Proc. 4th Intern. Conf. on Industrial Robots, pp. 251-260, 1974, propose a method for control of dual-arm robots in a master/slave manner. T. Ishida, Force Control in Coordination of Two Arms, Proc. 5th Intern. Conf. on Artificial Intelligence, pp. 717-722, 1977, considers parallel and rotational transfer of loads using dual-arm robots. S. Fujii et al., Coordinated Computer Control of a Pair of Manipulators, Proc. 4th World Congress on Theory of Machines and Mechanisms, pp. 411-417, Newcastle-upon-Tyne, England, 1975, suggest a technique for dual-arm control based on the method of virtual reference. C. Alford et al., Coordinated Control of Two Robot Arms, Proc. Intern. Conf. on Robotics, pp. 468-473, Atlanta, Ga., 1984, describe a method for coordinated control of two arms. Y. Zheng et al., Constrained Relations Between Two Coordinated Industrial Robots, Proc. Machine Intelligence Conf., Rochester, N.Y., 1985 and Computation of Input Generalized Forces for Robots with Closed Kinematic Chain Mechanisms, IEEE Journal of Robotics and Automation, pp. 95-103, Vol. RA-1, No. 2, 1985, obtain constrained relations and control laws for two coordinated arms. T. Tarn et al., Coordinated Control of Two Robot Arms, Proc. IEEE Intern. Conf. on Robotics and Automation, pp. 1193-1202, San Francisco, Calif., 1986, employ the "Global" linearization technique for dual-arm control. S. Hayati, Hybrid Position/Force Control of Multi-Arm Cooperating Robots, Proc. IEEE Intern. Conf. on Robotics and Automation, pp. 82-89, San Francisco, Calif., 1986, and in pending U.S. Patent Application Method and Apparatus for Hybrid Position/Control of Multi-Arm Cooperating Robot, filed Mar. 21, 1988, Ser. No. 06/845,991 proposes a method for controlling dual-arm robots based on partitioning the load between the arms. A. Koivo, Adaptive Position-Velocity-Force Control of Two Manipulators, Proc. 24th IEEE Conf. on Decision and Control, pp. 1529-1532, Ft. Lauderdale, Fla., 1985, suggests an adaptive control technique for dual-arm robots using the self-tuning approach. J. Lim et al., On a Control Scheme for Two Cooperating Robot Arms, Proc. 24th IEEE Conf. on Decision and Control, pp. 334-337, Ft. Lauderdale, Fla., 1985, describes a positional control scheme for two cooperating robot arms.
Some recent results of single-arm adaptive control are reported in the following papers: H. Seraji, Adaptive Control of Robotic Manipulators, JPL Engineering Memorandum 347-182, January, 1986; H. Seraji, Direct Adaptive Control of Manipulators in Cartesian Space, Journal of Robotic Systems, February, 1987 (to appear); and H. Seraji, Adaptive Forces and Position Control of Manipulators, JPL Engineering Memorandum 347-192, October, 1986.
The above-identified articles, to the extent that they are properly considered prior art, do not teach or suggest that a dual-arm adaptive control system, nor such a system having adaptive hybrid control of each arm independently. Moreover, only in this application is it taught that a multi-arm adaptive control system is reliably operable so long as the load's inter-arm cross-coupling is treated as though that cross-coupling were an externally caused disturbance. The adaptive hybrid control system of this invention can compensate for that cross-coupling because of the novel force and/or position control laws as herein defined.
There are certain key differences between my single-arm invention's approach and the conventional hybrid control approach of Raibert and Craig, referred to above. Firstly, in my single-arm invention, the force or position control problems are formulated in the Cartesian space with the end-effector Cartesian forces as the manipulated variables; whereas in Raibert and Craig, the problems are formulated in the joint space. The single-arm invention's formulation results in computational improvement since inverse Jacobians are not required for the controllers' operation. Secondly, the single-arm invention's hybrid system operates on the measured variables so as to produce the position and force variables that need to be controlled; whereas in Raibert and Craig, a selection matrix and its complement are used after formulation of tracking errors. In summary, the Raibert and Craig disclosure simply does not teach or suggest the novel concepts of my invention.